Warts are typically small, rough, and hard growths that are similar in colour to the rest of the skin. They typically do not result in symptoms except when on the bottom of the feet where they may be painful. While they usually occur on the hands and feet they can also affect other locations. One or many warts may appear. They are not cancerous. Warts are caused by infection with a type of human papillomavirus (HPV). Factors that increase the risk include use of public showers, working with meat, eczema, and a low immune system. The virus is believed to enter the body through skin that has been damaged slightly. A number of types exist including: common warts, plantar warts, filiform warts, and genital warts. Genital warts are often sexually transmitted. Without treatment, most types of warts resolve in months to years. A number of treatments may speed resolution including salicylic acid applied to the skin and cryotherapy. In those who are otherwise healthy they do not typically result in significant problems. Treatment of genital warts differs from that of other types. Warts are very common, with most people being infected at some point in their life. The estimated current rate of non-genital warts among the general population is 1–13%. They are more common among young people. Estimated rates of genital warts in sexually active women is 12%. Warts have been described at least as far back as 400 BC by Hippocrates.